1. Field of the Invention
The present invention relates generally to the control of common-mode signal levels.
2. Description of the Related Art
Pipelined analog-to-digital signal converters are attractive choices for high-speed, high-resolution signal-processing applications. By breaking down the generation of a desired number of digital bits into a cascade (pipeline) of low resolution signal converters, pipelined converter systems achieve high resolution at sampling speeds that are difficult, if not impossible, to realize with other converter systems.
In pipelined systems, each pipeline stage (whether sampler or converter stage) passes an output signal to a succeeding stage for further processing. The accuracy of the conversion process directly corresponds to the accuracy of these output signals. In order to preserve this accuracy, the output signals must be generated with amplifiers that closely control the common-mode level of the output signals at the predetermined level of a common-mode reference voltage Vcm. In addition, these amplifiers must control the common-mode level with bandwidths that are sufficient to reduce perturbations of the common-mode level that would otherwise have been induced by transients in the analog input signal.
Although amplifier structures have been provided to satisfy these amplifier requirements, they generally operate with structures (e.g., capacitors and switching transistors) that require substantial amplifier current so that they significantly degrade converter efficiency.